Compared with other secondary batteries such as nickel-cadmium batteries and nickel hydrogen batteries, lithium ion batteries have excellent characteristics such as a higher energy density, no memory effect, and a longer cycle life. For these reasons, lithium ion batteries have been widely used as a power source of portable electronic devices.
In the past few years, on the other hand, defects such as smoking or firing of battery packs using lithium ion batteries have arisen. The cause is considered to be a short circuit between electrodes due to mixed foreign metallic particles inside such lithium ion batteries. Currently, however, no foreign metallic particles have been found in batteries in which such defects have arisen and characteristics of batteries themselves could have caused such defects.
A battery capacity measuring method using impedance spectrum analysis is known as an example of a technology to measure such battery characteristics. Also, for example, the characteristic factor digitization method of batteries using a nonlinear equivalent circuit model is known.
However, the above technologies are both used to determine a battery capacity and are not methods of determining characteristics regarding safety of batteries.
Knowing electrical characteristics regarding safety of batteries is considered to be extremely important also for preventing defects caused by batteries. Moreover, if good batteries can be distinguished from bad ones by a simple method, defects may be considered to be preventable.
However, no method has been known to evaluate characteristics regarding safety of not only lithium ion batteries, but also other types of batteries. Thus, a simple evaluation method that can distinguish good batteries from bad ones is desired.
Under the current circumstances, as described above, there is a problem that it is difficult to evaluate characteristics regarding safety of batteries by a simple method to distinguish good batteries from bad ones.